On Fri, 3 Jul 2009, Rafael J. Wysocki wrote: > > ["error" isn't a good name. The return value would be 0 to indicate > > the request was accepted and queued, or 1 to indicate the device is > > already active. Or perhaps vice versa.] > > Why do you insist on using positive values? Also, there are other situations > possible (like run-time PM is disabled etc.). I think we should use positive values to indicate situations that aren't the "nominal" case but also aren't errors. This simplifies error checking in drivers. For example, you wouldn't want to print a debugging or warning message just because the device happened to be active already when you called pm_runtime_resume. > I don't really like the async_action idea, as you might have noticed. Do you mean that you don't like the field, or that you don't like its name? > > > Thus, it seems reasonable to remember what type of a request is pending > > > (i don't think we can figure it out from the status fields in 100% of the > > > cases). > > > > That's what the async_action field in my proposal is for. > > Ah. Why don't we just use a request type field instead? "A rose by any other name..." > In fact, we can use a 2-bit status field (RPM_ACTIVE, RPM_SUSPENDING, > RPM_SUSPENDED, RPM_RESUMING) and a 2-bit request type field > (RPM_REQ_NONE, RPM_REQ_IDLE, RPM_REQ_SUSPEND, RPM_REQ_RESUME). That's the same as my 0, ASYNC_IDLE, ASYNC_SUSPEND, ASYNC_RESUME. > Additionally, we'll need an "idle notification is running" flag as we've aleady > agreed, but that's independent on the status and request type (except that, I > think, it should be forbidden to set the request type to RPM_REQ_IDLE if > this flag is set). I don't see why; we can allow drivers to queue an idle notification from within their runtime_idle routine (even though it might seem pointless). What we should forbid is calling pm_runtime_idle when the flag is set. > That would pretty much suffice to represent all of the possibilities. > > I'd also add a "disabled" flag indicating that run-time PM of the device is > disabled, an "error" flag indicating that one of the > ->runtime_[suspend/resume]() callbacks has failed to do its job and > and an int field to store the error code returned by the failing callback (in > case the failure happened in an asynchronous routine). Sure -- those are all things in the current design which should remain. As well as the wait_queue. > That's fine, we'd also need to wait for running callbacks to finish too. And > I'm still not convinced if we should preserve requests queued up before the > system sleep. Or keep the suspend timer running for that matter. This all does into the "to-be-determined" category. :-) > Could you please remind me what timer_expiration is for? It is the jiffies value for the next timer expiration, or 0 if the timer isn't pending. Its purpose is to allow us to correctly reschedule suspend requests. Suppose the timer expires at about the same time as a new pm_schedule_suspend call occurs. If the timer routine hasn't queued the work item yet then there's nothing to cancel, so how do we prevent a suspend request from being added to the workqueue? Answer: The timer routine checks timer_expiration. If the value stored there is in the future, then the routine knows it was triggered early and it shouldn't submit the work item. Also (a minor benefit), before calling del_timer we can check whether timer_expiration is nonzero. > So, at a high level, the pm_request_* and pm_schedule_* functions would work > like this (I'm omitting acquiring and releasing locks): > > pm_request_idle() > * return -EINVAL if 'disabled' is set or 'runtime_error' is set > * return -EAGAIN if 'runtime status' is not RPM_ACTIVE or 'request type' is > RPM_REQ_SUSPEND or 'usage_count' > 0 or 'child_count' > 0 We should allow the status to be RPM_RESUMING. > * return -EALREADY if 'request type' is RPM_REQ_IDLE No, return 0. > * return -EINPROGRESS if 'idle notification in progress' is set No, go ahead and schedule another idle notification. > * change 'request type' to RPM_REQ_IDLE and queue up a request to execute > ->runtime_idle() or ->runtime_suspend() (which one will be executed depends > on 'request type' at the time when the work function is run) More simply, just queue the work item. > * return 0 > > pm_schedule_suspend() > * return -EINVAL if 'disabled' is set or 'runtime_error' is set > * return -EAGAIN if 'usage_count' > 0 or 'child_count' > 0 > * return -EALREADY if 'runtime status' is RPM_SUSPENDED > * return -EINPROGRESS if 'runtime status' is RPM_SUSPENDING The last two aren't right. If the status is RPM_SUSPENDED or RPM_SUSPENDING, cancel any pending work and set the type to RPM_REQ_NONE before returning. In other words, cancel a possible pending resume request. > * if suspend timer is pending, deactivate it This step isn't needed here, since you're going to restart the timer anyway. > * if 'request type' is not RPM_REQ_NONE, cancel the work Set timer_expiration = jiffies + delay. > * set up a timer to execute pm_request_suspend() > * return 0 > > pm_request_suspend() > * return if 'disabled' is set or 'runtime_error' is set > * return if 'usage_count' > 0 or 'child_count' > 0 > * return if 'runtime status' is RPM_SUSPENDING or RPM_SUSPENDED First cancel a possible pending resume request. If the status is RPM_RESUMING or RPM_ACTIVE, cancel a possible pending timer (and set time_expiration to 0). > * if 'request type' is RPM_REQ_IDLE, change it to RPM_REQ_SUSPEND and return > * change 'request type' to RPM_REQ_SUSPEND and queue up a request to > execute ->runtime_suspend() > > pm_request_resume() > * return -EINVAL if 'disabled' is set or 'runtime_error' is set > * return -EINPROGRESS if 'runtime status' is RPM_RESUMING Or RPM_ACTIVE. > * return -EALREADY if 'request type' is RPM_REQ_RESUME For these last two, first cancel a possible pending suspend request and a possible timer. Should we leave a pending idle request in place? And return 1, not an error code. > * if suspend timer is pending, deactivate it The timer can't be pending at this point. > * if 'request type' is not RPM_REQ_NONE, cancel the work At this point, 'request type' can only be RPM_REQ_NONE or RPM_REQ_RESUME. In neither case do we want to cancel it. > * return 1 if 'runtime status' is RPM_ACTIVE See above. > * change 'request type' to RPM_REQ_RESUME and queue up a request to > execute ->runtime_resume() Queue the request only if the state is RPM_SUSPENDED. > * return 0 > > Or did I miss anything? I think this is pretty close. It'll be necessary to go back and reread the old email messages to make sure this really does everything we eventually agreed on. :-) Similar outlines apply for pm_runtime_suspend, pm_runtime_resume, and pm_runtime_idle. There is an extra requirement: When a suspend or resume is over, if 'request type' is set then schedule the work item. Doing things this way allows the workqueue thread to avoid waiting around for the suspend or resume to finish. Also, when a resume is over we should schedule an idle notification even if 'request type' is clear, provided the counters are 0. Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
